Reconfigurable Manufacturing Implementation

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Each pixel is adjustable in the Z-axis direction independently from the other pixels, and is referred to in terms of its location in the upper die with the notation U(x,y) location, and L(x,y) for the lower part. Example is shown in Figure 1 for the upper part. In the implemented design, each pixel represents a 9.8x9.8 mm squared section steel bar with a 40 mm length. Each pixel is supported by an M-8 bolt that controls its Z-location.

Figure 2. Example for pins’ arrangements for a concaved part, (a) upper and (b) lower die halves

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The pixels movement along the Z-axis is coordinated between the lower and upper set of pixels such that each pixel in each set corresponds to another pixel from the other set. The pixels are referred to in terms of their x & y locations. Each pixel in the upper and lower die part has the same magnitude of Z coordinate but in opposite directions. Hence, the upper and lower parts of the die will take the desired shape of the final part. An example of a concaved forming is used here and is shown in Figure 2.

The die was designed and manufactured in the manufacturing lab at the UAE University. A section drawing of the die is shown in Figure 3. It shows the upper and lower parts of the die as well as the pixels orientation in both sections. The pixels are lined up in a matrix where each pixel is adjusted by an individual bolt. This allows for independent adjustment of the pixels’ heights. This independent adjustment can theoretically produce large number of shapes. The upper and lower pixel’s heights will complement each other to the flat level of the pixels.The heights of all pixels in both the upper and lower die parts have to be calculated based on the part to be manufactured profile. The process of calculating the pixels’ heights can be automated and integrated with standard Computer Aided Engineering tools.

3. Example and Results

An example of concaved part using a 8x8 FlexDie is employed to demonstrate the idea. The calculated heights using MS Excel are shown in Table 1 below for the upper and lower die halves. The surface of the part is an upper surface of a sphere with radius R, and is defined by Equations (1), (2), and (3) as indicated below.

(1)

For a given radius R and a set of coordinates (x, y), the first two equations in (1) can be solved for , which is then used in the third equation to calculate the pixel height z.

Based on the calculated heights for all pixels, the pins’ heights are adjusted individually using the corresponding screws and thus controlling pixels’ desired heights. Figure 4 shows the back view of the die. The setup of the distances is done in reference to the zero level of all the pixels. The upper pixels and lower pixels are adjusted to equal distances in opposite directions as shown in Figure 5 (a) and (b). The pixels are allowed to slide freely as the bolts behind them are adjusted to raise or lower each individual pixel. The setup in Figure 5 (a) and (b) was done for a 0.5 mm thick aluminum sheet. The dimensions of the effective area is the summation of the individual pixels in both x and y direction. As the heights are adjusted to different levels, the resulting part will be different. The number of bolts for this setup is 64 for each part, which make it time consuming to do the setup manual. In the next version of this die, the setup will be automated to reduce the setup time and increase accuracy. After adjusting the heights of all pixels for the example part, the die upper and lower parts are shown in Figure 5.

Figure 3. Schematic drawing for a section along the upper and lower die parts

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Once the heights of the bolts of both parts of the die are setup and the workpiece is prepared and placed in the die; the die is pressed on the workpiece to form it. A manual press was used to form a 0.5 mm and a 0.8 mm sheet metal parts. Pictures of the resulting parts are shown in Figure 6. It was noticed that the 0.5 mm part showed some fractures especially near the side pixels, Figure 6 (a). Investigation of those fractures revealed that the height of the pixels near the edges needs to be less to reduce the individual pixel drawing distance. The heights were adjusted at one of the edges that showed the max fracture, and the fractures reduced substantially. More investigation is undergoing to optimize on an adjusting factor to the calculated height shown in Table 1 (a) and (b) above. For the 0.8 mm sheet, fractures were much less.

Table 1. (a) and (b) shows calculated heights of the pins in the two halves of the die for the considered example

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Tables index

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The pictures in Figure 7 (a) and (b) show a reduction in part fracture when using a sheet blanket to compensate for the rough pixels’ size and sharp edges. The blanket used is 0.5 mm thick of textile material. The results show smooth consistent curvature of the part.

Figure 4. The screw-side of the die

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Figure 5. (a) and (b) upper and lower parts of the die for the example part

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4. Conclusion and Future Work

In this paper a reconfigurable manufacturing concept has been demonstrated through the idea of using a flexible die to manufacture variety of curved metal sheet parts. In FlexDie the authors examined squared section pins controlled by a set of screws. Although in the presented design we limited ourselves to using pins with square cross section and flat square face, the used pins could be selected from assortment of square pins with inclined faces with standard angles (e.g. 15°, 30°, 45°, 60°, 75°). This added flexibility will increase the smoothness of the generated curved die topology.

The process is done manually in the presented experiment where the deformation and shape of the workpiece is controlled manually. The preliminary results obtained are promising and work is continuing in our lab to improve the resolution and capability of the process. More applications are understudy where the control of the pixels is done via the CAD system. Work is undergoing for manufacturing different versions of the FlexDie for different applications. Also, in the next generation of this FlexDie, the CAD model will be post processed to send a signal to a PLC controlled mechanism or robot to typeset pins and to control their Z- coordinates and lock then in place.

Figure 6. A part manufactured using the FlexDie

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Figure 7. A part produced using a blanket to smooth the sharp edges

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